Die extraction method

ABSTRACT

Provided is a die extraction method, comprising the following steps: removing solder balls; polishing a front side of the sample to remove a part on a front side of the target die, and retain a part of a die attach film (DAF) layer on the front side of the target die and a bonding wire located in the part; attaching the front side of the sample to the polishing jig and flattening the sample and the polishing jig by the flattener; polishing the back side of the sample to remove a part on a back side of the target die, and retain a DAF layer on the back side of the target die; removing the DAF and a packaging material remaining on the sample to obtain the target die; and attaching the back side of the target die to a glass slide, thus completing extraction of the target die.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of International PatentApplication No. PCT/CN2021/106332, filed on Jul. 14, 2021, which claimspriority to Chinese Patent Application No. 202011145942.0, filed withthe Chinese Patent Office on Oct. 23, 2020 and entitled “DIE EXTRACTIONMETHOD”. International Patent Application No. PCT/CN2021/106332 andChinese Patent Application No. 202011145942.0 are incorporated herein byreference in their entireties.

TECHNICAL FIELD

The present disclosure relates to the field of integrated circuitinspection technologies, and in particular to a die extraction method.

BACKGROUND

In an integrated circuit packaging structure, in order to increase acapacity per unit area, packaging is usually performed by stacking dies.At present, in the inspection of the integrated circuit packagingstructure, the location of failure hot points can only accurately locatea die at the current layer, and when a die stacked at the lower layerfails, the failure point cannot be located. In order to realize thefailure location of the lower-layer die, the electrical properties of adie pad (a circuit board for soldering integrated circuit dies) aredetected in cooperation with a probe under a condition that the originalelectrical properties of the die at the lower layer must be keptunchanged, the die is extracted, and then failure location can becarried out. According to an existing die extraction method, multiplestacked dies are separated by soaking with high-temperature fumingnitric acid for a long time (above 1 h). Due to an ultra-thin thickness(about 50 μm) of the stacked dies, it will lead to problems of diecracking and die pad corrosion, resulting in failure to detectelectrical properties. In order to alleviate the above-mentionedproblems, although the stacked dies can be polished to the target die atthe lower layer to reduce the soaking time, traditional hand-heldpolishing will still cause a problem of a large step difference (about30 μm or more) on a surface of a sample.

SUMMARY

One of the main objectives of the present disclosure is to overcome atleast one of the above-mentioned drawbacks of a prior art, and toprovide a die extraction method that can maintain the integrity of thephysical structure of a sample and keep the electrical propertiesunchanged.

In order to achieve the foregoing objectives, the embodiments of thepresent disclosure adopt the following technical solution:

According to one aspect of the present disclosure, there is provided adie extraction method for extracting a target die from multiple dielayers in an integrated circuit sample, the method including thefollowing steps:

removing solder balls from a back side of the sample;

attaching the back side of the sample to a polishing jig, and flatteningthe sample and the polishing jig by a flattener;

polishing a front side of the sample to remove a part on a front side ofthe target die, and retain a part of a die attach film (DAF) layer onthe front side of the target die and a bonding wire located in the part;

attaching the front side of the sample to the polishing jig andflattening the sample and the polishing jig by the flattener;

polishing the back side of the sample to remove a part on a back side ofthe target die, and retain a DAF layer on the back side of the targetdie;

removing the DAF and a packaging material remaining on the sample toobtain the target die; and

attaching the back side of the target die to a glass slide, thuscompleting extraction of the target die.

BRIEF DESCRIPTION OF DRAWINGS

By considering the following detailed description of the exemplaryembodiments of the present disclosure in conjunction with theaccompanying drawings, various objectives, features, and advantages ofthe present disclosure will become more apparent. The accompanyingdrawings are only schematic illustrations of the present disclosure, andare not necessarily drawn to scale. In the drawings, like referencenumerals refer to the same or similar part. Among the drawings,

FIG. 1 is a schematic structural diagram of an integrated circuit in astep of a die extraction method according to the present disclosure;

FIG. 2 is a schematic structural diagram of an integrated circuit in astep of a die extraction method according to the present disclosure;

FIG. 3 is a schematic structural diagram of an integrated circuit in astep of a die extraction method according to the present disclosure;

FIG. 4 is a schematic structural diagram of an integrated circuit in astep of a die extraction method according to the present disclosure;

FIG. 5 is a schematic structural diagram of an integrated circuit in astep of a die extraction method according to the present disclosure;

FIG. 6 is a schematic structural diagram of an integrated circuit in astep of a die extraction method according to the present disclosure;

FIG. 7 is a schematic structural diagram of an integrated circuit in astep of a die extraction method according to the present disclosure;

FIG. 8 is a schematic structural diagram of an integrated circuit in astep of a die extraction method according to the present disclosure;

FIG. 9 is a schematic structural diagram of an integrated circuit in astep of a die extraction method according to the present disclosure;

FIG. 10 is a schematic structural diagram of an integrated circuit in astep of a die extraction method according to the present disclosure;

FIG. 11 is a schematic diagram of a back side of an integrated circuitin the step shown in FIG. 2 ;

FIG. 12 is a schematic partial top view of FIG. 4 ;

FIG. 13 is a partial enlarged view of an integrated circuit in the stepshown in FIG. 5 ; and

FIG. 14 is a schematic top view of a bonding wire of a target die atmultiple stages in the step shown in FIG. 5 .

REFERENCE NUMERALS

-   -   100 sample;    -   101 reference point;    -   110 substrate;    -   111 solder ball;    -   120 die;    -   121 target die;    -   122 bonding wire;    -   130 DAF;    -   140 packaging material;    -   150 polyimide film;    -   200 polishing jig;    -   210 hot melt adhesive;    -   300 flattener;    -   310 base;    -   320 pressing plate;    -   330 pressure sensor.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments embodying the features and advantages of thepresent disclosure will be described in detail in the followingdescription. It should be understood that the present disclosure canhave various changes in different embodiments, without departing fromthe scope of the present disclosure, and the descriptions and drawingstherein are essentially for illustrative purposes, not to limit thepresent disclosure.

In the following description of the different exemplary embodiments ofthe present disclosure, it is made with reference to the accompanyingdrawings which form a part of the present disclosure and in whichdifferent exemplary structures, systems and steps that can implementvarious aspects of the present disclosure are shown by way of example.It should be understood that other specific solutions of components,structures, exemplary devices, systems, and steps can be used, andstructural and functional modifications can be made without departingfrom the scope of the present disclosure. Moreover, although the terms“above”, “between”, “within”, etc. may be used in this specification todescribe different exemplary features and elements of the presentdisclosure, these terms are used herein for convenience only, forexample, according to the directions of the examples described in thedrawings. Nothing in this specification should be understood asrequiring a specific three-dimensional direction of the structure tofall within the scope of the present disclosure.

Referring FIGS. 1 to 10 , schematic structural diagrams of an integratedcircuit in multiple steps of a die extraction method according to thepresent disclosure are respectively shown representatively. In thisexemplary embodiment, the die extraction method according to the presentdisclosure is described using an example of extracting a target die froman integrated circuit packaging structure having a stacked diestructure. It is easy for those skilled in the art to understand that,in order to apply the relevant design of the present disclosure to theextraction of die structures of other types of integrated circuits orother processes, various modifications, additions, substitutions,deletions or other changes have been made to the following specificimplementations. These changes are still within the scope of theprinciple of the die extraction method of the present disclosure.

As shown in FIGS. 1 to 10 , this embodiment takes the target die 121which is at a middle layer of multiple stacked die layers 120 as anexample for description. In other embodiments, the present disclosurecan also be applied to extraction of a die 120 closest to a front sideor back side of an integrated circuit packaging structure (hereinafterreferred to as the sample 100) from the multiple stacked die layers 120.With reference to FIGS. 11 to 14 , FIG. 11 representatively shows aschematic diagram of a back side of an integrated circuit in the stepshown in FIG. 2 ; FIG. 12 representatively shows a schematic partial topview of FIG. 4 ; FIG. 13 representatively shows a partial enlarged viewof an integrated circuit in the step shown in FIG. 5 ; and FIG. 14representatively shows a schematic top view of a bonding wire 122 of thetarget die 121 at multiple stages in the step shown in FIG. 5 . In thefollowing, the process, sequence and relationship of the main steps ofthe die extraction method according to the present disclosure will bedescribed in detail in conjunction with the above-mentioned drawings.

As shown in FIGS. 1 to 10 , in this embodiment, the die extractionmethod according to the present disclosure can extract the target die121 from the multiple die layers 120 of the integrated circuit sample100. The die extraction method according to the present disclosure atleast includes the following steps:

removing solder balls 111 from a back side of the sample 100;

attaching the back side of the sample 100 to a polishing jig 200, andflattening the sample 100 and the polishing jig 200 by a flattener 300;

polishing a front side of the sample 100 to remove a part on a frontside of a target die 121, and retain a part of a DAF layer 130 on thefront side of the target die 121 and a bonding wire 122 located in thepart;

attaching the front side of the sample 100 to the polishing jig 200, andflattening the sample 100 and the polishing jig 200 by flattener 300;

polishing the back side of the sample 100 to remove a part on the backside of the target die 121, and retain a DAF layer 130 on the back sideof the target die 121;

removing the DAF layer 130 and a packaging material 140 remaining on thesample 100 to obtain the target die 121; and

attaching the back side of the target die 121 to a glass slide, thuscompleting extraction of the target die 121.

Based on the foregoing industrial design, in the die extraction methodaccording to the present disclosure, the integrated circuit sample 100is flatly attached to the polishing jig 200; in cooperation withpolishing, a polishing position can stay within a short distance fromthe target die 121; and by virtue of short-term soaking with anacid-base solution, the target die 121 can be extracted completely withthe original electrical properties unchanged, which is contributive toaccurate location of a failure point under the assistance of a probe ina consequent inspection process.

As shown in FIG. 1 , FIG. 1 representatively shows a schematicstructural diagram of a sample 100 from which a target die 121 is to beextracted. Specifically, the sample 100 includes a substrate 110 (suchas a PCB (Printed Circuit Board) substrate), solder balls 111, multipledie layers 120, multiple DAF layers 130, bonding wires 122, and apackaging material 140. The solder balls 111 are arranged on the backside of the substrate 110 (i.e., the back side of the sample 100). Themultiple die layers 120 are stacked on the front side of the substrate110, and two adjacent dies 120 are respectively bonded by a DAF layer130. The target die 121 to be extracted is at a middle layer of themultiple die layers 120. Each die layer 120 is connected to the frontside of the substrate 110 through the bonding wire 122 respectively. Thepackaging material 140 covers the front side of the substrate 110 andthe multiple die layers 120.

Continuing from the above, an existing process for extracting the die120 is mainly used to deal with the die 120 at the current layer, butcannot locate the failure hot points of the dies 120 at the middle andbottom layers. For the dies 120 at the middle and bottom layers, if theexisting extraction process is adopted, during the inspection of theextracted target die 121, since space needs to be reserved for probeinspection, a height difference of about 50 μm between the bonding wire122 and the surface of the target die 121 in the existing process cannotmeet the inspection requirements of the probe.

As shown in FIG. 2 , FIG. 2 representatively shows a schematicstructural diagram of a sample 100 in a step of “removing solder balls111”. Specifically, the sample 100 after the solder balls 111 areremoved includes a substrate 110, multiple die layers 120, multiple DAFlayers 130, bonding wires 122, and a packaging material 140.

For the step of “removing solder balls 111”, in some embodiments, thesolder balls 111 can be removed by an electric soldering iron. In otherembodiments, the solder balls 111 can also be removed by other processesor devices, and it will not be limited to this embodiment.

As shown in FIG. 11 , in some embodiments, after the solder balls 111are removed, the sample 100 can be flattened, for example, referencepoints 101 are selected for polishing until a difference incorresponding thickness between any two of the reference points 101 isless than or equal to a third threshold. The third threshold is athickness difference between points of the sample 100 after the solderballs 111 are removed and the sample 100 is flattened. For details,reference can be made to the process description of flattening thesample 100 in the following other steps. In other embodiments, in orderto make the sample 100 after the solder balls 111 are removed more evenin thickness and more flat, the number of reference points selected onthe surface of the sample can also be less than five, or more than five,and at least two. In addition, the at least two reference points may notinclude a central reference point located at a geometric center positionon the back side of the sample 100, and it will not be limited to thisembodiment.

Based on the process design of selecting the reference points on theback side of the sample 100 and polishing the back side of the sample100 accordingly, in an exemplary embodiment, the third threshold may bewithin a range of 8 μm to 12 μm, such as 8 μm, 9.5 μm, 11.8 μm, 12 μm,and the like. In other embodiments, the third threshold can also be lessthan 8 μm, or can be greater than 12 μm, such as 7.9 μm, 12.2 μm, andthe like, and is not limited to this embodiment.

As shown in FIG. 11 , based on a process design of selecting one centralreference point and four edge reference points on the back side of thesample 100, in this embodiment, an example where a cross section of thesample 100 is roughly rectangular, that is, the back side of the sample100 is roughly rectangular is described, the central reference point canbe located at the center of the corresponding rectangle of the back sideof the sample 100, and the four edge reference points can be located atfour corners on the back side of the sample 100.

Based on the process design of selecting the reference points on theback side of the sample 100 and polishing the back side of the sample100 accordingly, in this embodiment, in the above-mentioned step ofpolishing the back side of the sample 100, the back side of the sample100 can be polished with sandpaper with a particle size of P1500 ormore.

As shown in FIG. 3 , FIG. 3 representatively shows a schematicstructural diagram of a sample 100 and a polishing jig 200 in a step of“attaching the back side of the sample 100 to the polishing jig 200”.Specifically, the back side of the sample 100 attached to the polishingjig 200 includes a substrate 110, multiple die layers 120, multiple DAFlayers 130, bonding wires 122, and a packaging material 140. The backside of the sample 100 is attached to the polishing jig 200.

Optionally, as shown in FIG. 3 , for the step of “attaching the backside of the sample 100 to the polishing jig 200”, in this embodiment,the back side of the sample 100 can be attached to the polishing jig 200through a hot melt adhesive 210.

As shown in FIG. 4 , FIG. 4 representatively shows a schematicstructural diagram of a sample 100, a polishing jig 200 and a flattener300 in a step of “flattening the sample 100 and the polishing jig 200 bya flattener 300”. Specifically, when the back side of the sample 100 isattached to the polishing jig 200, the polishing jig 200 is placed on abase 310 of the flattener 300, a pressure is applied to the front sideof the sample 100 many times by a pressing plate 320 of the flattener300, and the polishing jig 200 is rotated by an angle between twoconsecutive pressure applications to flatten the sample 100 and thepolishing jig 200.

Optionally, as shown in FIG. 12 , for the step of “flattening the sample100 and the polishing jig 200 by the flattener 300”, in this embodiment,the polishing jig 200 can rotate by a same angle each time, and theangle the polishing jig 200 rotates each time can be calculated as 360°divided by a number of times of pressure application. For example, thepolishing jig 200 can be rotated 6 times, and the angle of each rotationis approximately 60°. In other embodiments, the polishing jig 200 may berotated more than six times, or less than six times, and at least twice.For example, the polishing jig 200 can be rotated eight times, and theangle the polishing jig 200 rotates each time is approximately 45°.Furthermore, the angle the polishing jig 200 rotates each time may notbe completely the same, or may be completely different, and can beflexibly adjusted according to a requirement for flattening the sample100 and the polishing jig 200, and it will not be limited to thisembodiment.

Optionally, as shown in FIG. 12 , for the step of “flattening the sample100 and the polishing jig 200 by the flattener 300”, in this embodiment,the pressure applied by the pressing plate 320 to the sample 100 may bewithin a range of 10 N to 20 N, such as 10 N, 12 N, 15 N, 20 N, and thelike. In other embodiments, the pressure applied by the pressing plate320 to the sample 100 can also be less than 10 N, or can be greater than20 N, such as 9 N, 22 N, and the like, and it will not be limited tothis embodiment.

Optionally, as shown in FIG. 4 , a pressure sensor 330 may be arrangedon the pressing plate 320 to monitor the pressure applied by thepressing plate 320 to the front side of the sample 100 in real time.

Optionally, as shown in FIG. 12 , for the step of “flattening the sample100 and the polishing jig 200 by the flattener 300”, in this embodiment,time of each pressure application by the pressing plate 320 can bewithin a range of 3 s to 6 s, such as 3 s, 4.5 s, 5.2 s, 6 s, and thelike. In other embodiments, the time of each pressure application by thepressing plate 320 can be less than 3 s or can be greater than 6 s, suchas 2.8 s, 6.5 s, and the like, and it will not be limited to thisembodiment.

Optionally, in this embodiment, after the back side of the sample 100 isattached to the polishing jig 200 and the sample 100 and the polishingjig 200 are flattened by the flattener 300, at least two referencepoints can be selected on the front side of the sample 100, acorresponding thickness of the sample 100 corresponding to each ofreference points is measured by a height measuring device, and a part ofthe front side of the sample 100 where one, with a relatively largecorresponding thickness, of the reference points is located is polisheduntil a difference in the corresponding thickness between any two of thereference points is less than or equal to a second threshold. The secondthreshold is a thickness difference between the points of the sample 100flattened by the flattener 300. A specific process for selecting thereference points on the front side of the sample 100 in this step canrefer to the following process step of selecting reference points on theback side of the sample 100 and it will not be repeated here.

Based on the process design of selecting the reference points on thefront side of the sample 100 and polishing the front side of the sample100 accordingly, in this embodiment, the second threshold may be withina range of 8 μm to 12 μm, such as 8 μm, 9 μm, 10.7 μm, 12 μm, and thelike. In other embodiments, the second threshold can also be less than 8μm, or can be greater than 12 μm, such as 7.6 μm, 12.1 μm, and the like,and it will not be limited to this embodiment.

As shown in FIG. 5 , FIG. 5 representatively shows a schematicstructural diagram of a sample 100 and a polishing jig 200 in the stepof “polishing a front side of the sample”. Specifically, the sample 100with the polished front side includes a substrate 110, a remaining partof the die layers 120, a remaining part of the DAF layers 130, aremaining part of the bonding wires 122 and a remaining part of thepackaging material 140. The remaining dies 120 include the target die121 and other die layers 120 located below the target die 121 (i.e.,between the target die 121 and the substrate 110). The remaining DAFlayer 130 includes the remaining part of a DAF layer 130 on the frontside (the side away from the substrate 110) of the target die 121 inaddition to the DAF layers 130 located between the remaining adjacentdies 120.

Optionally, for the step of “polishing a front side of the sample 100”,in this embodiment, a distance between an end, far away from the targetdie 121, of the bonding wire 122 retained on the front side of thetarget die 121 and the target die 121 may be within a range of 5 μm to20 μm, such as 5 μm, 7.5 μm, 10.5 μm, 20 μm, and the like. The aboveprocess design can prevent damage to the probe due to a too long bondingwire 122 or a short circuit caused by the tilt of the adjacent probe,and also can provide a larger area for the application of the probe,thus improving the success rate of the probe. In other embodiments, thedistance between the end of the bonding wire 122 retained on the frontside of the target die 121 and the target die 121 may also be greaterthan 20 μm, such as 20.5 μm and the like and it will not be limited tothis embodiment.

Based on the design that the distance between the end of the bondingwire 122 retained on the front side of the target die 121 and the targetdie 121 may be within a range of 5 μm to 20 μm, the distance maypreferably be 10 μm in this embodiment. Specifically, the distance of 10μm is selected in this embodiment because the probe needs to be placedon a pad of the target die 121 for measuring the electrical propertiesof the pad. For existing pad structures of the die 120, some pads havebonding wires thereon 122 while others do not. Because the probes arethin and a distance between the probes is relatively short, if thebonding wire 122 is too far from the pad, on the one hand the probe maybe damaged, and on the other hand, uneven height may cause the probes toconnect together and cause a short circuit. In other embodiments,according to the structures of different target die 121 and thestructures of different probes, the distance between the end of thebonding wire 122 retained on the front side of the target die 121 andthe target die 121 can also be adjusted, but the distance must begreater than or equal to 5 μm for preventing a case where the target dieis scratched due to the too short distance during the polishing process.

Optionally, for the step of “polishing the front side of the sample100”, in this embodiment, a thickness of the remaining part of a DAFlayer 130 retained on the front side of the target die 121 may be withina range of 5 μm to 20 μm, such as, 5 μm, 7.5 μm, 10.5 μm, 20 μm, and thelike. In other embodiments, the thickness of the remaining part of a DAFlayer 130 retained on the front side of the target die 121 may also beless than 5 μm, or may be greater than 20 μm, such as 4.8 μm, 20.5 μm,and the like and it will not be limited to this embodiment.

Specifically, for the step of “polishing a front side of the sample100”, in this embodiment, the following steps may be specifically usedto polish the front side of the sample 100:

fixing the polishing jig 200 attached to the back side of the sample 100to a mechanical arm of a polishing machine, and adjusting the polishingjig 200 so that the polishing jig 200 and a polishing disc of thepolishing machine are level; and

converting a change in pressure value into a distance unit by using apressure sensor installed on the mechanical arm of the polishingmachine, based on which a thickness of a polished part of the front sideof the sample 100 is monitored in real time.

When testing a flatness of the sample 100 in the step of “removing thesolder balls 111”, as shown in FIG. 2 , an X value can be measured, anda Y value refers to the thickness of the packaging material 140 of thesample 100 (the thickness of the packaging material 140 covering the die120 at the top. The Y value is known, and an error is within y (y is,for example, 30 μm). On this basis, the front side of the sample 100 ispolished with a piece of 30 μm diamond sandpaper until X−Y+y=Z, then thepolishing is stopped, and whether the front side of the sample 100 ispolished to a DAF layer 130 on the front side of the target die 121 canbe observed under a microscope, for example, it can be distinguishedunder the microscope according to a color difference (the packagingmaterial 140 and the DAF layer 130 are different in color). The X valuerefers to the overall thickness of the sample 100, the X value can beobtained by measurement, and the Y value is known because in thepackaging process, the thickness of each die 120 and the thickness ofeach DAF layer 130 are both known. Therefore, according to a number ofother die layers and DFA layers above the target die, the thickness ofthe part, to be removed by polishing, of the sample 100 above the targetdie 121 can be roughly calculated, and in order to further ensure thereliability of the process, the error y of 30 μm is reserved in thisembodiment, that is, an extra thickness of 30 μm is reserved to preventexcessive polishing during the process of polishing the front side ofthe sample.

The polishing is continued with a piece of 6 μm diamond sandpaper, thepolishing is stopped every time the Z value decreases by 3 μm, and achange in the sectional shape of the bonding wire 122 connected to thefront side of the target die 121 is observed under a microscope.

The polishing is continued with a piece of 3 μm diamond sandpaper for,for example, 3 s at a polishing speed of, for example, 60 r/s, thepolishing is then stopped, and a then shape similar to the sectionalshape of the bonding wire 122 at position D in FIG. 14 can be observedunder a microscope; at this time, a distance from the front side of theremaining part of the DAF layer 130 to the surface of the target die 121can be ensured, that is, the thickness of the remaining part of the DAFlayer 130 is approximately within a range of 5 μm to 20 μm.

Continuing from the above, as shown in FIG. 13 , for the above-mentionedspecific steps of polishing the front side of the sample 100, fourpositions, position A, position B, position C and position D, on thebonding wire 122 connected to the front side of the target die 121 areselected from top to bottom when the bonding wire 122 is close to thetarget die 121. As the DAF layer 130 is polished during the polishingprocess, the sectional shapes of the bonding wire 122 corresponding tothe above four positions observed under a microscope are not certainlyapproximated to the four shapes in FIG. 14 . Accordingly, theabove-mentioned shapes can be observed under a microscope to determinethe shape of the remaining part of the bonding wire 122, that is, toassist in determining the thickness of the remaining part of the DAFlayer 130.

Optionally, for the step of “polishing a front side of the sample 100”,in this embodiment, when the front side of the sample 100 is polished,the thickness of the remaining part of the DAF layer 130 on the frontside of the target die 121 can be measured in real time. When thethickness of the remaining part of the DAF layer 130 reaches athreshold, the polishing is stopped. The threshold is the thickness ofthe remaining part of the DAF layer 130 mentioned above.

Optionally, in this embodiment, after the front side of the sample 100is polished, the sample 100 may be flattened. For example, fivereference points 101 may be selected on the front side of the sample100, and the five reference points 101 include a central reference pointand four edge reference points. The central reference point is locatedat a geometric center position of the front side of the sample 100, andthe edge reference points are located at edge positions of the frontside of the sample 100. On this basis, a corresponding thickness of thesample 100 corresponding to each of reference points 101 is measured bya height measuring device, and a part of the front side of the sample100 where one, with a relatively large corresponding thickness, of thereference points 101 is located is polished until a difference in thecorresponding thickness between any two of the reference points 101 isless than or equal to a threshold. The threshold is a thicknessdifference between the points of the sample 100 having the front sidepolished during the flattening process. In other embodiments, in orderto make the sample 100 having the front side polished more even inthickness and more flat, the number of reference points selected on thesurface of the sample can also be less than five, or more than five, andat least two. In addition, the at least two reference points may notinclude central reference points located at the geometric centerposition on the front side (or the back side) of the sample 100, and itwill not be limited to this embodiment.

As shown in FIG. 6 , FIG. 6 representatively shows a schematicstructural diagram of a sample 100 and a polishing jig 200 in a step of“attaching the sample 100 to the polishing jig 200 on the front side”.Specifically, the sample 100 attached to the polishing jig 200 on thefront side includes a substrate 110, a remaining part of the die layers120, a remaining part of the DAF layers 130, a remaining part of thebonding wires 122 and a remaining part of the packaging material 140.The sample 100 is attached to the polishing jig 200 on the front surfacepolished in the foregoing step. That is, the sample 100 is attached tothe polishing jig 200 on the back surface; after being flattened by theflattener 300, the front side is polished by polishing equipment; thenthe sample 100 is removed from the polishing jig 200 and subjected toother leveling treatments; after that, the sample 100 is attached to thepolishing jig 200 on the polished front side.

Optionally, as shown in FIG. 6 , for the step of “attaching the frontside of sample 100 to the polishing jig 200”, in this embodiment, thefront side of the sample 100 can be attached to the polishing jig 200through the hot melt adhesive 210.

Optionally, in this embodiment, after the front side of the sample 100is attached to the polishing jig 200 and the sample 100 and thepolishing jig 200 are flattened by the flattener 300, at least tworeference points can be selected on the back side of the sample 100, acorresponding thickness of the sample 100 corresponding to each ofreference points is measured by a height measuring device, and a part ofthe back side of the sample 100 where one, with a relatively largecorresponding thickness, of the reference points is located is polisheduntil a difference in the corresponding thickness between any two of thereference points is less than or equal to a first threshold. The firstthreshold is a thickness difference between various positions of thefront side of the sample 100 attached to the polishing jig 200. Aspecific process for selecting the reference points on the back side ofthe sample 100 in this step can refer to the foregoing process step ofselecting the reference points on the sample 100 and it will not berepeated here.

Based on the process design of selecting the reference points on thefront side of the sample 100 and polishing the front side of the sample100 accordingly, in this embodiment, the first threshold may be within arange of 20 μm to 40 μm, such as 20 μm, 25 μm, 32 μm, 40 μm, and thelike. In other embodiments, the first threshold can also be less than 20μm, or can be greater than 40 μm, such as 18 μm, 41 μm, and the like,and it will not be limited to this embodiment.

As shown in FIG. 7 , FIG. 7 representatively shows a schematicstructural diagram of a sample 100 and a polishing jig 200 in the stepof “polishing the back side of the sample 100”. FIG. 8 shows a schematicstructural diagram of a sample 100 having the back side polished afterremoval from a polishing jig 200. Specifically, the sample 100 havingthe back side polished includes a target die 121, a DAF layer 130 on aback side of the target die 121, a remaining part of a DAF layer 130 ona front side of the target die 121, a remaining part of a bonding wire122 connected to the target die 121, and a remaining part of a packagingmaterial 140. In addition, the sample 100 removed from the polishing jig200 further includes a polyimide film 150 on the front side of thetarget die 121 (not shown in the aforementioned figures) and a hot meltadhesive 210 remaining on the front side of the sample 100.

It should be noted that after the front side of the sample 100 ispolished, the hot melt adhesive 210 attached between the back side ofthe sample 100 and the polishing jig 200 can be melted by heating, andthen the front side of the sample 100 is attached to the polishing jig200 (polished). During the above process, the sample 100 can be turnedover with tweezers. After turning over, the substrate 110 on the backside of the sample 100 will also be polished away. When the back side ispolished to expose a DAF layer 130 at the bottom of the sample 100, thepolishing can be stopped. The die 120 and the DAF layer 130 can bedistinguished because the die 120 and the DAF layer 130 are different incolor.

Optionally, for the step of “polishing the back side of the sample 100”,in this embodiment, whether the back side of the sample 100 is polishedto a DAF layer 130 on the back side of the target die 121 can beobserved under a microscope, for example, it can be distinguished underthe microscope according to a color difference (the packaging material140 and the DAF layer 130 are different in color).

Optionally, in this embodiment, after the front side of the sample 100is polished, the sample 100 can be flattened. For example, a method ofselecting reference points on the back side of the sample 100 can beused. For the specific process, reference can be made to the foregoingprocess steps of selecting reference points on the sample 100, and itwill not be repeated here.

As shown in FIGS. 9 and 10 , in this embodiment, the removing the DAFlayer 130 and the packaging material 140 remaining on the sample 100 mayspecifically include the following steps:

soaking the target die 121 with fuming nitric acid to remove the DAF 130and the packaging material 140 (such as epoxy resin), and also to removea hot melt adhesive 210 used for attaching the sample 100 to thepolishing jig 200;

rinsing the target die 121 with deionized water;

soaking the target die 121 with ethylenediamine to remove the polyimidefilm 150 from the surface of the target die 121; and

rinsing the target die 121 again with deionized water.

As shown in FIG. 9 , FIG. 9 representatively shows a schematicstructural diagram of the sample 100 in the step of “removing the DAFlayer 130 and the packaging material 140”. Specifically, the sample 100having the DAF layer 130 and the packaging material 140 removed includesthe target die 121 and the polyimide film 150 remaining on the frontside of the target die 121, and further includes a remaining part of abonding wire 122 connected to the target die 121.

Optionally, for the step of “soaking the target die 121 with fumingnitric acid”, in this embodiment, a temperature of the fuming nitricacid may be within a range of 60° C. to 80° C., for example, 65° C., 68°C., 75° C., 80° C., and the like. In other embodiments, the temperatureof the fuming nitric acid can also be lower than 60° C., or higher than80° C., such as 58° C., 81° C., and the like and it will not be limitedto this embodiment.

For the step of “soaking the target die 121 with fuming nitric acid”,based on the process design that the temperature of the fuming nitricacid is within a range of 60° C. to 80° C., in this embodiment, thetemperature of the fuming nitric acid may be 60° C.

Optionally, for the step of “soaking the target die 121 with fumingnitric acid”, in this embodiment, the time of soaking with the fumingnitric acid may be within a range of 30 s to 50 s, such as 31 s, 33 s,41 s, 50 s, and the like. In other embodiments, the time of soaking withthe fuming nitric acid can be less than 30 s, or can be more than 50 s,such as 28 s, 51 s, and the like, and it will not be limited to thisembodiment.

For the step of “soaking the target die 121 with fuming nitric acid”,based on the process design that the time of soaking with the fumingnitric acid is within a range of 30 s to 50 s, in this embodiment, thetime of soaking with the fuming nitric acid may be 30 s. Accordingly,due to a short time of contact with an acid-base solution, structures ofthe pad and the bonding wire will not be corroded, thereby ensuring thatthe probe can detect the electrical properties of the target die 121.

Optionally, for the step of “rinsing with deionized water the target die121 soaked with the fuming nitric acid”, in this embodiment, the time ofrinsing with the deionized water may be more than 10 s, such as 10 s, 11s, 15 s, 20 s, and the like. In other embodiments, the time of rinsingwith the deionized water may also be less than 10 s, such as 9 s, and itwill not be limited to this embodiment.

Optionally, for the step of “soaking the target die 121 withethylenediamine”, in this embodiment, a temperature of theethylenediamine may be within a range of 50° C. to 80° C., such as 55°C., 66° C., 72° C., 80° C., and the like. In other embodiments, thetemperature of the ethylenediamine can also be lower than 50° C., orhigher than 80° C., such as 49° C., 82° C., and the like and it will notbe limited to this embodiment.

For the step of “soaking the target die 121 with ethylenediamine”, basedon the process design that the temperature of the ethylenediamine iswithin a range of 50° C. to 80° C., in this embodiment, the temperatureof the ethylenediamine may be 50° C.

Optionally, for the step of “soaking the target die 121 withethylenediamine”, in this embodiment, the time of soaking with theethylenediamine may be within a range of 30 s to 50 s, such as 32 s, 35s, 42 s, 50 s, and the like. In other embodiments, the time of soakingwith the ethylenediamine can be less than 30 s, or can be more than 50s, such as 29 s, 52 s, and the like, and it will not be limited to thisembodiment.

For the step of “soaking the target die 121 with ethylenediamine”, basedon the process design that the time of soaking with the ethylenediamineis within a range of 30 s to 50 s, in this embodiment, the time ofsoaking with the ethylenediamine may be 30 s. Accordingly, due to ashort time of contact with an acid-base solution, the structure of thepad will not be corroded, thereby ensuring that the probe can detect theelectrical properties of the target die 121.

Optionally, for the step of “rinsing with deionized water the target die121 soaked with the ethylenediamine”, in this embodiment, the time ofrinsing with deionized water may be more than 10 s, such as 10 s, 13 s,16 s, 22 s, and the like. In other embodiments, the time of rinsing withdeionized water may also be less than 10 s, such as 8 s, and it will notbe limited to this embodiment.

Optionally, for the step of “attaching the target die 121 to a glassslide”, in this embodiment, the back side of the target die 121 may beattached to the glass slide by a hot melt adhesive. Based on the aboveprocess design, during the testing by the probe, the target die 121 canbe easily fixed, and a stress acting on the target die 121 by the probecan be relieved.

It should be noted here that the die extraction methods shown in thedrawings and described in this specification are only a few examples ofmany die extraction methods that can adopt the principle of the presentdisclosure. It should be clearly understood that the principle of thepresent disclosure is by no means limited to any details or any steps ofthe die extraction methods shown in the drawings or described in thisspecification.

In summary, in the die extraction method according to the presentdisclosure, the integrated circuit sample is flatly attached to thepolishing jig; in cooperation with polishing, a polishing position canstay within a short distance from the target die 121; and by virtue ofshort-term soaking with an acid-base solution, the target die can beextracted completely with the original electrical properties unchanged,which is contributive to accurate location of a failure point under theassistance of a probe in a consequent inspection process.

The exemplary embodiments of the die extraction method according to thepresent disclosure are described and/or illustrated above in detail.However, the embodiments of the present disclosure are not limited tothe specific embodiments described herein. On the contrary, theconstituent parts and/or steps of each embodiment can be usedindependently and separately from other constituent parts and/or stepsdescribed herein. Each constituent part and/or step of one embodimentcan also be used in combination with other constituent parts and/orsteps of other embodiments. During the explanation of theelements/constituent parts/etc. described and/or illustrated herein, theterms such as “one”, “a”, “the” and the like are intended to mean thatthere exists one or more elements/constituent parts/etc. The terms“including”, “comprising”, and “having” are intended to be inclusive andmean that there may be additional elements/constituent parts/etc. otherthan the listed elements/constituent parts/etc. In addition, the terms“first” and “second” in the claims and specification are used only asmarks, and are not numerical limitations on their objects.

Although the die extraction method of the present disclosure has beendescribed according to different specific embodiments, those skilled inthe art will appreciate that the implementation of the presentdisclosure can be modified within the spirit and scope of the claims.

What is claimed is:
 1. A die extraction method for extracting a target die from multiple die layers in an integrated circuit sample, the method comprising the following steps: removing solder balls from a back side of the integrated circuit sample; attaching the back side of the integrated circuit sample to a polishing jig, and flattening the integrated circuit sample and the polishing jig by a flattener; polishing a front side of the integrated circuit sample to remove a part on a front side of the target die, and retain a part of a die attach film (DAF) layer on the front side of the target die and a bonding wire located in the part; attaching the front side of the integrated circuit sample to the polishing jig and flattening the integrated circuit sample and the polishing jig by the flattener; polishing the back side of the integrated circuit sample to remove a part on a back side of the target die, and retain a DAF layer on the back side of the target die; removing the DAF and a packaging material remaining on the integrated circuit sample to obtain the target die; and attaching the back side of the target die to a glass slide, thus completing extraction of the target die.
 2. The die extraction method according to claim 1, wherein in the step of polishing the front side of the integrated circuit sample, a distance between an end, far away from the target die, of the bonding wire retained on the front side of the target die and the target die is within a range of 5 μm to 20 μm.
 3. The die extraction method according to claim 1, wherein when the front side of the integrated circuit sample is polished, a thickness of a DAF layer retained on the front side of the target die is within a range of 5 μm to 20 μm.
 4. The die extraction method according to claim 1, wherein after the front side of the integrated circuit sample is attached to the polishing jig and the integrated circuit sample and the polishing jig are flattened by the flattener, at least two reference points are selected on the back side of the integrated circuit sample, a corresponding thickness of the integrated circuit sample corresponding to each of the reference points is measured by a height measuring device, and a part of the back side of the integrated circuit sample where one, with a relatively large corresponding thickness, of the reference points is located is polished until a difference in the corresponding thickness between any two of the reference points is less than or equal to a first threshold.
 5. The die extraction method according to claim 4, wherein the first threshold is within a range of 20 μm to 40 μm.
 6. The die extraction method according to claim 1, wherein the back side of the integrated circuit sample is attached to the polishing jig by a hot melt adhesive.
 7. The die extraction method according to claim 1, wherein when the back side of the integrated circuit sample is attached to the polishing jig, the polishing jig is placed on a base of the flattener, a pressure is applied to the front side of the integrated circuit sample a plurality of times by a pressing plate of the flattener, and between two consecutive pressure applications rotated the polishing jig by an angle, in order to flatten the integrated circuit sample and the polishing jig.
 8. The die extraction method according to claim 7, wherein at least one of the polishing jig rotates by a same angle each time, and the angle is calculated as 360° divided by a number of times of pressure application; the pressure applied by the pressing plate is within a range of 10 N to 20 N; or time of each pressure application by the pressing plate is within a range of 3 s to 6 s.
 9. The die extraction method according to claim 1, wherein after the back side of the integrated circuit sample is attached to the polishing jig and the integrated circuit sample and the polishing jig are flattened by the flattener, at least two reference points are selected on the front side of the integrated circuit sample, a corresponding thickness of the integrated circuit sample corresponding to each of the reference points is measured by a height measuring device, and a part of the front side of the integrated circuit sample where one, with a relatively large corresponding thickness, of the reference points is located is polished until a difference in the corresponding thickness between any two of the reference points is less than or equal to a second threshold.
 10. The die extraction method according to claim 9, wherein the second threshold is within a range of 8 μm to 12 μm.
 11. The die extraction method according to claim 1, wherein after the solder balls are removed, at least two reference points are selected on the back side of the integrated circuit sample, a corresponding thickness of the integrated circuit sample corresponding to each of the reference points is measured by a height measuring device, and a part of the back side of the integrated circuit sample where one, with a relatively large corresponding thickness, of the reference points is located is polished until a difference in the corresponding thickness between any two of the reference points is less than or equal to a third threshold.
 12. The die extraction method according to claim 11, wherein the third threshold is within a range of 8 μm to 12 μm.
 13. The die extraction method according to claim 1, wherein the removing the DAF and the packaging material remaining on the integrated circuit sample comprises the following steps: soaking the target die with fuming nitric acid to remove the DAF and the packaging material; rinsing the target die with deionized water; soaking the target die with ethylenediamine to remove a polyimide film from a surface of the target die; and rinsing the target die again with deionized water.
 14. The die extraction method according to claim 13, wherein at least one of a temperature of the fuming nitric acid is within a range of 60° C. to 80° C.; time of soaking with the fuming nitric acid is within a range of 30 s to 50 s; a temperature of the ethylenediamine is within a range of 50° C. to 80° C.; time of soaking with the ethylenediamine is within a range of 30 s to 50 s; time of first rinsing with the deionized water is more than 10 s; or time of second rinsing with the deionized water is more than 10 s.
 15. The die extraction method according to claim 1, wherein the back side of the target die is attached to the glass slide by a hot melt adhesive. 